Polymorphonuclear neutrophils must respond to multiple exogenous stimuli to proceed through the complex transformation from quiescence to activated phenotypes. The plasma membrane is the interface where this transformation must be initiated. Recent work has shown that plasma membranes are heterogeneous structures containing discrete regions, "lipid raft microdomains", enriched in glycosphingolipids, cholesterol, lipid-anchored receptors, and signaling molecules. Selective partitioning into lipid rafts appears to be a key mechanism for imposing organization on the distribution of proteins in the plasma membrane, thereby compartmentalizing discrete functions within the plasma membrane and, in essence, creating a syntax that translates otherwise dissociated signaling effectors into a meaningful language of signal transduction. The central hypothesis underlying this proposal is that the composition, structural integrity, and spatial distribution of lipid raft microdomains critically regulate key processes in neutrophil activation. Our preliminary studies of human neutrophils have shown that lipid rafts: i) spatially compartmentalize and selectively regulate neutrophil activation signaling, ii) selectively influence cellular responsiveness to proinflammatory agonists, and iii) regulate signal propagation during cell migration. The long-term objective of this project is to determine how the function and composition of lipid raft microdomains regulate the antimicrobial and proinflammatory functions of neutrophils. The short-term objectives are to: i) determine the mechanisms by which lipid rafts influence agonist-specific signal transduction, ii) determine how lipid rafts regulate the production and release of reactive oxygen intermediates, iii) determine how lipid rafts influence the expression, distribution, and function of (32 integrins, and iv) determine how lipid rafts control cellular polarity and calcium signaling during non-directional and chemotaxin-driven migration. Hopefully, targeting the function of lipid raft microdomains will engender new therapeutic strategies for enhancing antimicrobial defenses and suppressing the deleterious effects of acute inflammation.